Add --uber option to jar, war tasks

[alandipert]

The uber task is notoriously slow because it dumps static, exploded dependencies into the fileset on every build. It does this so subsequent jar or war tasks can see all the files that need to go into the jar. See #94 for a full discussion of the problem.

We think the best way to address the problem is by adding an --uber option to jar and war. That way, instead of needing to explode dependencies into the fileset, these tasks will pack dependencies directly into the jar/war being built, and only this "packed" jar goes on the fileset.

It doesn't feel like a great solution because we're loathe to fix a performance problem between two tasks by combining them. However, we can't think of a better way, and also think uber jars are probably a special case.

The plan is to have this in for 2.0, whether or not we should also deprecate the uber task is a good question. I think probably yes.

[bobby]

One datapoint: I've used the uber task with :as-jars to build zips with a lib/*.jar dir (uberzip?). So the capability of stashing jar'd deps on the fileset is a useful capability, whether tied to uber or not.

[micha]

I think the uber task is pretty fast now. Feel free to reopen if we want to revisit this.